The invention relates generally to seal strips for a suction roll in a papermaking machine in which the seal strips are each constructed from a plurality of individual strips joined together uniquely constructed in regards to the material and the ends of the individual strips which form a joint between the strips.
In the art of papermaking, various machines and steps are provided for forming paper webs beginning from a pulp slurry where one machine is commonly referred to as a fourdrinier machine. The papermaking machine typically includes a suction roll having a stationary suction box disposed centrally and internally of a perforated shell which is rotatably supported and rotates about the suction box. A vacuum source is connected to the suction box which draws the water or steam through the papermaking screen and perforated cylindrical shell for removal. The edges of the vacuum box are sealed against the rotating inside diameter of the cylindrical shell. Slot-like structures are typically formed along at least the two outside edges of the vacuum box for holding seal strips such as shown in U.S. Pat. Nos. 4,714,523 and 2,714,839. The suction boxes range in length up to 34 feet. Prior seal strips have been provided in lengths equal to the length of the suction box. However, this has provided considerable difficulties in shipping the seal strips, particularly overseas. These seal strips have been manufactured mainly by an extrusion process where a seal strip is extruded having a length corresponding to the length of the suction box slot. As a result of the problems of shipping seal strips of a great length, the extruded seal strips have been cut into sections. The shorter sections may be packaged and shipped more conveniently. However, cutting the extruded seal strips into sections has resulted in considerable sealing problems at the ends of the sections which must be joined together end to end across the length of the suction box slot. Prior seal strips have been cut with square cut ends to form a flat abutting surface, and have also been cut at an angle. The angular cut has several problems, one including a tendency of adjoining sealing strips to ride past each other. The square cut joints often do not seal well. Another problem with the prior suctional seal strips is that the edges of the joints, particularly from cutting, often chip and break resulting in deterioration in the sealing of the joint.
Sectional sealing gaskets with interfitted joints are known such as disclosed in U.S. Pat. Nos. 3,738,670 and 3,231,289. In addition, it has been known to utilize joints, including curved hooks, in rod packings such as disclosed in U.S. Pat. Nos. 1,502,524 and 1,017,674. However, these uses and structures are not compatible in the joining together of longitudinal strips in a papermaking machine environment.
Accordingly, an important object of the invention is to provide a seal strip for a papermaking machine suction roll which may be joined together with other seal strips to form a composite seal strip throughout the entire width of a suction box slot of the suction roll which has good wear characteristics as a seal against the rotating surface of a perforated cylindrical shell and also has good sealing characteristics at the joints between the individual seal strips joined together across the slot.
Another object of the invention is to provide a seal strip for a papermaking machine suction box which may be joined together by other seal strips to form a composite seal strip of greater length across the full width of a suction box wherein the seal strip is molded and includes uniquely formed ends which form a highly effective seal between the seal strips.
Another object of the present invention is to provide a seal strip which may be joined together with other seal strips to form a composite seal strip of greater length throughout the entire width of a papermaking machine suction box slot which is molded and which the ends are uniquely constructed to form an effective seal between the seal strips and reduce breakage of the ends of the seal strips to maintain the integrity of the sealed joint.